U.S. patent application number 14/039033 was filed with the patent office on 2014-10-30 for charge pump capacitor assembly with silicon etching.
This patent application is currently assigned to Robert Bosch GmbH. The applicant listed for this patent is Robert Bosch GmbH. Invention is credited to John M. Muza.
Application Number | 20140319658 14/039033 |
Document ID | / |
Family ID | 51788575 |
Filed Date | 2014-10-30 |
United States Patent
Application |
20140319658 |
Kind Code |
A1 |
Muza; John M. |
October 30, 2014 |
CHARGE PUMP CAPACITOR ASSEMBLY WITH SILICON ETCHING
Abstract
Charge pump capacitor assemblies and methods of manufacturing
the same. One charge pump capacitor assembly includes a charge pump
capacitor and a silicon substrate. The charge pump capacitor
includes: a silicon-based charge pump capacitor oxide layer, a
first terminal on a first side of the silicon-based charge pump
layer, a second terminal on a second side of the silicon-based
charge pump capacitor oxide layer opposite the first side, and a
field oxide layer mounted adjacent the second terminal. The charge
pump capacitor is coupled to the silicon substrate. The silicon
substrate is etched to reduce contact between the silicon substrate
and the field oxide layer.
Inventors: |
Muza; John M.; (Venetia,
PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Robert Bosch GmbH |
Stuttgart |
|
DE |
|
|
Assignee: |
Robert Bosch GmbH
Stuttgart
DE
|
Family ID: |
51788575 |
Appl. No.: |
14/039033 |
Filed: |
September 27, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61817523 |
Apr 30, 2013 |
|
|
|
Current U.S.
Class: |
257/632 ;
438/397 |
Current CPC
Class: |
H01L 27/0805 20130101;
H01L 27/0222 20130101; H02M 3/07 20130101; H01L 28/40 20130101;
H01L 29/0607 20130101 |
Class at
Publication: |
257/632 ;
438/397 |
International
Class: |
H01L 29/06 20060101
H01L029/06; H01L 49/02 20060101 H01L049/02 |
Claims
1. A charge pump capacitor assembly comprising: a charge pump
including a silicon-based charge pump capacitor oxide layer, a
first terminal on a first side of the silicon-based charge pump
layer, a second terminal on a second side of the silicon-based
charge pump layer opposite the first side, and a field oxide layer
mounted adjacent the second terminal; and a silicon substrate
coupled to the charge pump, wherein the substrate is etched to
reduce contact between the silicon substrate and the field oxide
layer.
2. The charge pump capacitor assembly of claim 1, wherein the
silicon substrate is etched to eliminate contact between the
silicon substrate and the field oxide layer.
3. The charge pump capacitor assembly of claim 1, wherein the first
terminal includes a metal contact.
4. The charge pump capacitor assembly of claim 1, wherein the first
terminal includes a surface of the charge pump capacitor oxide
layer on the first side.
5. The charge pump capacitor assembly of claim 1, wherein the
second terminal includes a metal contact.
6. The charge pump capacitor assembly of claim 1, wherein the
charge pump capacitor oxide layer is formed of silicon oxide.
7. The charge pump capacitor assembly of claim 1, wherein the
charge pump capacitor oxide layer is formed of silicon nitride.
8. A method of manufacturing a charge pump capacitor assembly, the
method comprising: forming a field oxide layer on a silicon
substrate; forming a first charge pump terminal on the field oxide
layer; forming a charge pump layer on top of the first terminal;
forming a second charge pump terminal on top of the charge pump
layer to create a charge pump between the first charge pump
terminal and the second charge pump terminal; and etching the
silicon substrate to reduce contact between the substrate and the
field oxide layer.
9. The method of claim 8, wherein etching the silicon substrate
includes etching the substrate to eliminate contact between silicon
substrate and the field oxide layer.
10. The method of claim 8, further comprising forming at least one
pressure relief hole through the field oxide layer, the first
charge pump terminal, the first charge pump terminal, the charge
pump layer, and the second charge pump terminal.
Description
RELATED APPLICATIONS
[0001] The present application claims priority to U.S. Provisional
Patent Application No. 61/817,523 filed Apr. 30, 2013, the entire
contents of which is incorporated by reference herein.
BACKGROUND
[0002] The present invention relates to microelectromechanical
system ("MEMS") devices, such as microphone systems, that include a
charge-pump component.
SUMMARY
[0003] Some MEMS microphones (e.g., included in cellular phones,
headsets, personal computers, etc.) include a charge pump to boost
the bias voltage applied to a capacitive sensor above the power
supply voltage. However, in some microphone systems, the
construction of a charge pump can result in a parasitic capacitance
in the field oxide layer. As a result, a larger amount of charge
pump current consumption is due to wasted charging and discharging
of a capacitor to ground.
[0004] Accordingly, embodiments of the invention provide charge
pump assemblies and methods of manufacturing the same. In
particular, one embodiment of the invention provides a charge pump
capacitor assembly. The charge pump capacitor assembly includes a
charge pump and a substrate. The charge pump includes a
silicon-based charge pump layer, a first terminal on a first side
of the silicon-based charge pump layer, a second terminal on a
second side of the silicon-based charge pump layer opposite the
first side, and a field oxide layer mounted adjacent the second
terminal. The charge pump is coupled to the substrate, and the
substrate is etched to reduce contact between the substrate and the
field oxide layer. In particular, the substrate is etched such that
the substrate does not provide a ground for the field oxide
layer.
[0005] Another embodiment of the invention provides a method of
manufacturing a charge pump capacitor assembly. The method includes
forming a field oxide layer on a substrate, forming a first charge
pump terminal on the field oxide layer, forming a charge pump layer
on top of the first terminal, and forming a second charge pump
terminal on top of the charge pump layer to create a charge pump
between the first charge pump terminal and the second charge pump
terminal. The method also includes etching the substrate to reduce
contact between the substrate and the field oxide layer.
[0006] Other aspects of the invention will become apparent by
consideration of the detailed description and accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a cross-sectional view of an existing charge pump
capacitor assembly.
[0008] FIG. 2 is a circuit schematic of the electrical operation of
the charge pump capacitor assembly of FIG. 1.
[0009] FIG. 3 is a cross-sectional view of a charge pump capacitor
assembly according to one embodiment of the invention.
[0010] FIG. 4 is a circuit schematic of the electrical operation of
the charge pump capacitor assembly of FIG. 3.
DETAILED DESCRIPTION
[0011] Before any embodiments of the invention are explained in
detail, it is to be understood that the invention is not limited in
its application to the details of construction and the arrangement
of components set forth in the following description or illustrated
in the following drawings. The invention is capable of other
embodiments and of being practiced or of being carried out in
various ways.
[0012] FIG. 1 schematically illustrates a cross-sectional view of
an existing charge pump capacitor assembly 90. The assembly 90
includes a charge pump capacitor 95 and a silicon substrate 98
(e.g., a p-type substrate). The charge pump capacitor 95 includes a
first charge pump terminal 101 and a second charge pump terminal
103. The first terminal 101 and the second terminal 103 are formed
on either side of a charge pump layer 105. The charge pump
capacitor oxide layer 105 is mounted on a field oxide layer 107
such that the field oxide layer 107 is positioned adjacent to the
second terminal 103. The charge pump capacitor 95 is coupled to the
silicon substrate 98.
[0013] FIG. 2 illustrates electrical operation of the charge pump
capacitor assembly 90. As illustrated in FIG. 2, the first terminal
101 acts as a first node 111 of the circuit. The second terminal
103 operates as a second node 113 while the charge pump capacitor
oxide layer 105 operates as a capacitor 115 between the first node
111 and the second node 113. Because the substrate 98 serves as a
ground 119 for the charge pump 95, the field oxide layer 107
operates as a parasitic capacitor 117 that is repeatedly charged
and discharged to ground 119. This repeated charging and
discharging results in significant power loss for the charge pump
95.
[0014] FIG. 3 schematically illustrates a cross-sectional view of a
charge pump capacitor assembly 190 according to one embodiment of
the invention. The assembly 190 includes a charge pump capacitor
195 and a silicon substrate 198 (e.g., a p-type substrate or an
n-type substrate). The charge pump capacitor 195 includes a first
charge pump terminal 201 and a second charge pump terminal 203
positioned on opposite sides of a charge pump layer 205, which is
positioned on a field oxide layer 207. In particular, the first
terminal 201 is formed on one side of the charge pump layer 205,
and the second terminal 203 is formed on an opposite side of the
charge pump capacitor oxide layer 205 that is adjacent the field
oxide layer 207. The charge pump capacitor 195 is coupled to the
silicon substrate 198. However, as illustrated in FIG. 3, a silicon
etch is performed in the substrate 198 to remove at least a portion
of the substrate 198 that would contact the field oxide layer 207.
Removing a portion of the substrate 198 that otherwise contacts the
field oxide layer 207 reduces the surface area between these
components, which results in less charge flow over the surface area
and, consequently, less energy loss. Also, in some embodiments,
there is no contact between the field oxide layer 207 and the
silicon substrate 198. Accordingly, in these embodiments, the
substrate 198 does not provide a ground for the field oxide layer
207. It should be understood that although the portion of the
substrate 198 is removed below the field oxide layer 207, oxides on
the side and on top of the charge pump capacitor 195 provide
mechanical stability for the assembly 190 and couple the charge
pump capacitor 195 to the substrate 198.
[0015] The charge pump capacitor oxide layer 205 is formed of
silicon oxide (SiO.sub.2), silicon nitride (SiN), and/or other
suitable material. In some constructions, the first terminal 201
and the second terminal 203 each include a metal contact. However,
in other constructions, the first terminal 201 simply includes the
top surface of the charge pump capacitor oxide layer 205, and the
second terminal 203 includes the junction of the charge pump
capacitor oxide layer 205 and a field oxide layer 207.
[0016] FIG. 4 illustrates electrical operation of the charge pump
capacitor assembly 190. As illustrated in FIG. 4, the first
terminal 201 serves as a first node 211 and the second terminal 203
serves as a second node 213. The charge pump capacitor oxide layer
205 acts as a capacitor 215 between the first node 211 and the
second node 213. However, because the silicon substrate 198 has
been etched to eliminate contact between the substrate 198 and the
field oxide layer 207, the substrate 198 does not provide a ground
for the circuit. In particular, the air gap formed by the etched
substrate 198 serves as a floating node 219. The field oxide layer
207 still operates as a parasitic capacitor 217 between the second
node 213 and the floating node 219. However, dominant current
consumption component in the charge pump capacitor assembly 90 are
removed in the charge pump capacitor assembly 190 and,
consequently, the electrical voltage gain of a MEMS sensor that is
driven by the charge pump 95 is improved.
[0017] To create the charge pump capacitor assembly 190, the field
oxide layer 207 is formed on the substrate 198. The second terminal
203 is formed on the field oxide layer 207 and the charge pump
capacitor oxide layer 205 is formed on top of the second terminal
203. The first terminal 203 is also formed on top of the charge
pump layer 205 to create the charge pump 195 between the first
terminal 201 and the second terminal 203. The substrate 198 is then
etched to reduce contact between the substrate 198 and the field
oxide layer 207. In some embodiments, the substrate 198 is etched
to eliminate contact between the substrate 198 and the field oxide
layer 207. It should be understood that the substrate 198 can be
etched at any point during the manufacturing process. Also, because
there is air below the field oxide layer 207 (due to the etched
portion of the silicon substrate 198), when the assembly 190 is
glued down under heat air pressure forms in the etched portion. If
the air pressure gets too great, it could crack or damage the
charge pump capacitor 195. Therefore, in some embodiments, a safety
pressure relief hole is formed in the charge pump capacitor 195
from the top to the bottom (e.g., through the first terminal 201,
the charge pump capacitor oxide layer 205, the second terminal 203,
and the field oxide layer 207) to release at least a portion of the
air pressure.
[0018] Thus, the invention provides, among other things, a charge
pump capacitor assembly that eliminates the substrate as a ground
by etching the substrate such that the field oxide layer does not
contact the substrate.
[0019] Various features and advantages of the invention are set
forth in the following claims.
* * * * *